The present invention relates to a system for the transmission and storage of medical images and more particularly to a system for the transmission, receipt and storage of cardiology related image sequences using a non-linear time sampling and compensated playback system wherein the images of interest are transmitted via conventional methods in a relatively short period of time to a remote location or facility to enable a cardiologist or other specialist to view the images of interest and provide a meaningful consultation to the requesting physician. Additionally, the present invention allows for the rapid transmission of the images of interest over networks or other existing data transmission mechanisms without burdening the system with lengthy and complicated transmissions.
Teleradiology involves the transmission of the images of interest to an off-site or remote location for medical diagnoses or consultation. The most common transmission scenario involves the transmission of the images of interest from a hospital to a physician's home or office. With the increase in managed care and the use of the family practitioner or internist as the gate-keeper, the need for medical consultation with specialists such as surgeons and cardiologists has also increased. For example, there is often a desire to have a cardiologist over-read another physician's angiographic studies to confirm the treatment approach. Additionally, it may be desirable for another physician to review the angiographic study to confirm the need for a surgical procedure or to recommend alternate approaches. Oftentimes it is not practical for the specialist to review the entire record of the medical procedure to verify primary care physician's diagnosis, either due to the specialists schedule or physical location. It is increasingly desirable to be able to transmit a representative record of the medical study to the specialist to enable the specialist to determine whether or not further care is advisable or to make a preliminary diagnosis and recommendation to the primary physician. Similarly, many managers and insurance companies prefer to review the records of a patient to determine if the proposed procedure is advisable. Finally, it may be advisable to store an abbreviated angiographic record at the physician's offices or in the hospital in the event that the patient needs emergency treatment or to serve as a representative medical record in liability matters.
The present invention generally relates to the transmission and storage of radiological images, such as those resulting from angiographic or venogram procedures. Angiography is a diagnostic technique for visualizing the anatomy of arteries in the human heart. A Venogram is a diagnostic procedure which enables the physician to evaluate the efficiency of the patient's heart by observing the wall motion of the patient's heart and evaluating the efficiency of the ejection of blood from the heart of the patient. The procedures are accomplished by inserting a catheter into the area of the artery or heart of interest and injecting an x-ray opaque dye into the artery or heart of the patient. At the same time, an x-ray system exposes the artery or heart, and images are detected on an image intensifier. The images are typically recorded on 35 mm film or digitally via a television camera and then subjected to an analog to digital conversion for display and analysis.
These cardiographic procedures represent special difficulties for the storage and transmission of meaningful images because the studies are very data intensive. For example, a typical angiographic image study consists of about ten imaging sequences which range from about 4 to 12 seconds and average about six seconds in length. In the United States, these images are typically captured at a frame speed of about 30 frames per second and at about 25 frames per seconds in European countries which use 50 Hz power. It is important to maintain the intensity of this type of image to allow the physician to provide an accurate diagnosis. Therefore, in the United States, these images are typically digitized in a 512 by 512 by 8 bit image matrix, although other resolution matrices are also possible. Therefore, the total digital data required to represent a typical angiographic study may be between about 500 MB to about 1,000 MB. With currently available transmission methods, the time necessary to transmit a complete study makes it impractical to transmit the entire study each time a consultation is appropriate or the physician desires to review relevant portions of the study later at his office or home.
A common method of reducing the amount of digital data stored from angiographic studies is to utilize compression techniques that take advantage of the redundancy in the images and reduce the overall size of the study data file. These compression techniques oftentimes significantly reduce the amount of data to be stored. The compression techniques typically fall within two general types, lossless and lossy. In lossless or errorless compression, the uncompressed data at the receiving end or data restoration end of the system is identical to the original data. In lossy compression, the exact original data image cannot be recreated at the receiving or data restoration end of the system. Additionally, many lossy compression techniques may introduce artifacts or other potential errors into the uncompressed images. Lossless compression can typically reduce the amount of data for a typical angiographic image by about two. Lossy compression techniques can produce much higher compression ratios at the expense of errors, distortion or artifacts in the uncompressed image. The introduction of errors into the uncompressed image is totally unacceptable to the medical community when angiographic images are transmitted. Due to the need for highly accurate images, lossy compression is typically not acceptable for angiographic images. Additionally, with currently available transmission methods, compression rates significantly greater than two are necessary to provide an economically feasible and practical transmission system.
In a commercially available system known as ANGIOCOMM from Quinton Instrument Company, each image sequence is A/D converted, filtered and written into the local memory of a data storage device. At the conclusion of the image sequence, the image data is immediately compressed and data reduced for storage on the local hard drive of the local data storage device. The stored data may be reviewed later on the local data storage device or other review stations which are interconnected with the local data storage device by a conventional local area network system. The data compression techniques used for data storage in the ANGIOCOMM system include circular blanking, compression, A/D filtering and/or time domain data reduction depending on the user's preferences and requirements. The circular blanking involves the blanking of the acquires image outside of the circle which represents valid image data so that the area outside the valid image data is not written to the file. This represents a lossless compression of about 1.18 to 1. The size of the acquired image data circle may be selected by the user and is ideally set slightly larger than the blanking conventionally provided by the X-ray system to ensure that no valid image data is lost. Further compression may be used to take advantage of the redundancies found in most X-ray images by using conventional compression techniques to compress the images in the X-Y direction based on the quality and harshness of the images to provide an additional compression in the range of about 2:1 or 3:1. Finally, a limited time domain data reduction algorithm is provided to undersample at the beginning and end of the image sequence and acquire full samples during the middle of the image sequence. This represents a further data compression of about 2:1. As a result of using each of these compression methods, the stored data files for the image sequences may be reduced by about 8:1. Although this is beneficial for the storage of image sequences, significantly higher compression rates are needed for the commercially viable transmission of image sequences and other large data files telephonically or via other network systems.
In U.S. Pat. No. 5,291,401 granted to Robinson, a teleradiology system is disclosed which is directed to the collection, transmission and reception of raw digital data from a radiological device. The system disclosed in this patent describes the transmission of slices of radiological images using an undisclosed compression technique that enables the receiving physician to subsequently filter and evaluate the images transmitted by the technician.
Because the transmission of angiographic images is preferably conducted by transmitting image sequences rather than individual slices which, may or may not represent the best available images or provide sufficient context for the specialist to adequately review the angiographic record of the patient, the system disclosed in this patent does not appear to represent a viable system for the use in cardiology or other data intensive areas of the medical industry.